The invention relates to a method for reproducing spatially distributed sounds of a multichannel audio signal.
Audio is an important medium for conveying any kind of information, especially sound direction information. Indeed, the human auditory system is more effective than the visual system for surveillance tasks. Thanks to the development of multichannel audio format, spatialization has become a common feature in all domains of audio: movies, video games, virtual reality, music, etc.
Typically, such sounds are mixed onto multiple audio channels, wherein each channel is fed to a dedicated loudspeaker. Distribution of a sound to the different channels is adapted to the configuration of the dedicated playback system (positions of the loudspeakers); so as to reproduce the intended directionality of said sound.
Multichannel audio streams thus require to be played back over suitable loudspeaker layouts. For instance, each of the channels of a five channel formatted audio signal is associated with its corresponding loudspeaker within a five loudspeaker array. FIG. 1 shows an example of a five channel loudspeaker layout recommended by the International Telecommunication Union (ITU) for the 5.1 surround sound configuration. There are a left loudspeaker L, right loudspeaker R, center loudspeaker C, surround left loudspeaker LS and surround right loudspeaker RS, arranged around a reference listening point O which is the recommended listeners position. With this reference listening point O as a center, the relative angular distances between the central directions of the loudspeakers are indicated.
A multichannel audio signal is thus encoded according to an audio file format dedicated to a prescribed spatial configuration where loudspeakers are arranged at prescribed positions to a reference listening point. Indeed, each time-dependent input audio signal of the multichannel audio signal is associated with a channel, each channel corresponding to a prescribed position of a loudspeaker.
If multichannel audio is played back over an appropriate sound system, i.e. with the required number of loudspeakers and correct angular distances between them, a normal hearing listener is able to detect the location of the sound sources that compose the multichannel audio mix. However, should the actual sound system exhibit inappropriate features, such as too few loudspeakers, or an inaccurate angular distance thereof, the directional information of the audio content may not be delivered properly to the listener.
Patent application WO2008/113428 discloses a technique a conversion between arbitrary multi-channel formats. An input multi-channel representation is converted into a different output multi-channel representation of a spatial audio signal. An intermediate representation of the spatial audio signal is derived, the intermediate representation having direction parameters indicating a direction of origin of a portion of the spatial audio signal. The output multi-channel representation of the spatial audio signal is generated using the intermediate representation of the spatial audio signal.